In a field service testing instrument, which supports line rates up to and above the 10 Gbps range, e.g. OC192, STM64, 10 GBE, 10GFC, and multiple OTN rates, it is desirable to enable the technician to select from among three common optical wavelengths, i.e. 1550 nm, 1310 nm, and 850 nm, for both transmitting and receiving test signals. Accordingly, conventional testing instruments require three lasers, one for generating signals in each of the aforementioned wavelengths, and two receivers, one for converting 850 nm optical test signals and one for converting both 1550 nm and 1310 nm optical test signals, although only one laser and one receiver are active at a time, i.e. the one the technician has selected. Each laser source and receiver is purchased in the form of a transceiver module, e.g. XFP or SFP module, thus three transceiver modules are required for each testing instrument. Each transceiver module accepts differential, e.g. 10 Gbps, signals to and from a SERDES transceiver device, thus up to three SERDES transceiver devices would normally be required for each testing instrument for transmitting and receiving. The SERDES transceiver device is physically large, consumes considerable power, and is expensive for a field service instrument.
A SERDES or serializer/deserializer is an integrated circuit (IC or chip) transceiver that converts parallel data to serial data and vice-versa. The transmitter section converts an n-bit parallel bus into a differential serial stream, and the receiver section converts a differential serial stream into an n-bit parallel bus. SERDES chips facilitate the transmission of parallel data between two points over serial streams, reducing the number of data paths and thus the number of connecting pins or wires required. Most SERDES devices are capable of full-duplex operation, meaning that data conversion can take place in both directions simultaneously. SERDES chips are used in Gigabit Ethernet systems, wireless network routers, fiber optic communications systems, and storage applications. Specifications and speeds vary depending on the needs of the user and on the application. SERDES devices are capable of operating at speeds in excess of 10 Gbps.
A conventional XFP arrangement is illustrated in FIG. 1, in which an XFP transceiver module 1 is plugged into a host cage assembly 2 mounted on a host circuit board 3. The host cage assembly 2 includes a front bezel 4, a cage receptacle 5, and a host electrical connector 6. The transceiver module 1 is inserted through an opening in the front bezel 4, and through an open front of the cage receptacle 5, until an electrical connector on the transceiver module 1 engages the host electrical connector 6. The cage receptacle 5 has an opening 7 in the upper wall thereof through which a heat sink 8 extends into contact with the transceiver module 1 for dissipating heat therefrom. A clip 9 is provided for securing the heat sink 8 to the cage receptacle 5 and thereby into contact with the transceiver module 1. With this arrangement, the heat sink 8 can be changed to suit the owners individual needs without changing the basic transceiver module 1.
The XFP transceiver module 1 is a hot pluggable, small form factor, serial-to-serial, data agnostic, multi-rate optical transceiver that supports Telecom and Datacom applications. Unlike a 4xXAUI transceiver module, e.g. Xenpak, which have a four-channel interface at 3.125 Gb/s, or other 10 Gb transceiver modules, which have 16-channel interfaces, the XFP transceiver module 1 features a 10 Gb/s 100 ohm differential I/O interface 11 (XFI). One end of the module 1 includes the XFI serial connector 11, which receives and transmits differential signals at 10 Gb/s, while the other end includes input and output optical connectors 12a and 12b, which comply with multiple 10 Gb/s Telecom and Datacom standards. The XFP module's transmitter side includes a clock and data recovery (CDR) section 13, which cleans up and re-times an output electrical signal, and a laser driver 14 and a laser 15, which converts the cleaned up electrical output signal to an optical signal. The receiver side includes a photodetector 16, e.g. PIN or APD receiver, which converts a 10 Gb/s input optical signal to an input electrical signal, and a CDR 17, which cleans up the input electrical signal before sending it to a SERDES 18, which is remote from the XFP module 1 on the host circuit board 3.
An object of the present invention is to overcome the shortcomings of the prior art by providing a system in which a plurality of differential transceiver, e.g. XFP or SFP, modules are driven by a single SERDES transceiver device.